Various types of systems have been used for controllably inflating and deflating vehicle tires during vehicle operation. Such systems typically include an air supply of pressurized air and controls for selectively increasing or decreasing an existing tire pressure, and for determining current tire pressures for each tire. The ability to selectively increase or decrease tire pressure is desirable in connection with optimizing the operation of the vehicle under widely changing conditions including weather, Vehicular load, terrain, and vehicular speed,
A wheel valve tire air pressurization system is typically used for heavy vehicles having sets of tires pressurized thought respective manifolds and respective air channels. The wheel valve system has a wheel valve connected to each respective tire. The wheel valve is disposed in the air channel between an axle seal and the tires. The wheel valve can be shut off by air channel evacuation and thereby does not apply a continuous air pressure within the air channel through the axle seals leading to the tires. During the evacuation period when the wheel valve is shut off, the seal is not subject to air pressure. The lack of air pressure tends to extend the life of the axle air seal. The wheel valve system has one or more air manifolds each connected to a respective air channel connected to a respective set of wheel valves each set respectively connected to a set of tires. Each manifold controls the air flow through a respective air channel which controls a set of wheel valves and therefore controls the air pressure in a respective set of tires. Thus, a multiple manifold system can independently control multiple sets of tires, including for example, a set of front steering tires, a set of power drive tires, and a set of rear trailer tires. Each set of tires may have a respective desired tire pressure for a given traveling condition including speed, load and terrain.
The use of multiple manifolds advantageously allows for simultaneous independent air pressurization adjustment of each set of tires, put disadvantageously requires the use of multiple manifolds. The wheel valve system has a cab mounted controller routing a cable of wires to each attached manifold. Thus, in a multiple manifold wheel valve system, there are disadvantageously a plurality of cables extending from the cab mounted controller. There exists a need to reduce the complexity of wheel valve systems. Further, the wheel valve system disadvantageously requires multiple manifolds to independently control the air pressure of multiple sets of tires.
One problem of prior system have included the inability to achieve inflation or deflation from one tire pressure to another with accuracy, and within a reasonable time period. It is desirable to provide a system which is efficient, minimizes operator involvement and obtains the required pressure accuracy within short inflating and deflating time periods. Complex flow control valves or valve orifice arrangements are not very effective to maintain and are undesirably expensive because small orifices tend to clog and are subjected to wear for reasons of high fluid velocities. Successful pressure monitoring systems are described in U.S. Pat. Nos. 4782,878 and 5,309,969, both here incorporated by reference as there full set forth.
Prior art automatic control systems also suffer from a control problem called "hunting" when attempting to reach a desired tire pressure for a given operating condition.
During a pressure inflation or deflation adjustment cycle, the system will either overshoot or undershoot the desired pressure generating wasteful repeated pressure adjustment cycles, before settling down to a stable pressure. Such systems produce long inflation and deflation times, inaccurate pressure adjustments and reduced reliability of operation. During an adjustment cycle, when dynamic pressure reaches the desired pressure, and the adjustment cycle is terminated, the air pressure may change to a stabilized static pressure which may not equal the desired pressure, which again, may cause the system to enter into another pressure adjustment cycle.
Prior systems also provide methods of eliminating hunting by shutting off the system in the dynamic closed loop operation with the use of pressure offset values to reduce overshooting and undershooting and to provide an a reduction in the inflation and deflation times. One problem associated with the prior system is the loss of pressure offset values when the system is turned off during vehicular parking. Another problem associated with the prior system are errors in the offset values because the offset values do not compensate for the difference between the sensed pressures at the time of terminating the adjustment cycle and the subsequent stabilized static pressure. Yet another problem of the prior offset corrections is the use of constant offset values even during changing operating conditions which require changing offset correction values to maintain system performance.
Prior systems have also failed to address the need to conveniently change system operating functions and parameters especially useful during testing of experimental and newly designed vehicles and tires. Furthermore, air systems have been installed in a plurality of different vehicle models each having respectively desired operating functions and parameters disadvantageously requiring the manufacture of a respective plurality of unique systems or the manufacture of systems with dedicated additional, but unnecessary, model selecting switches.
A continuous air pressurized system is typically used for controlling the tire air pressure in light vehicles through a single manifold and a respective air channel. Continuous pressurized tire systems have been in common use. Kalavitz, U.S. Pat. No. 4,583,566 shows an exemplar continuous pressurized air system. The continuously pressurized system continuously monitors and adjusts the tire pressure with the air channel being continuously pressurized. The continuous system operates a integral three position valve for inflation, deflation and shut off. A transducer continuously monitors the tire air pressure which is compared to a desired pressure and pressure band. When the monitored tire pressure is outside the pressure band about the desired pressure, a valve is actuated to inflate or deflate the tire pressure. Once the pressure falls with the desired pressure band, then the valve is shut off with a resulting continuous air pressure applied within the air channel. The axle seal is used to communicate air pressure from the inflation and deflation valves through the system to the tires. The higher the axle rpm speed under air pressure, the faster the axle seal wears leading to a failure. One problem associated with the continuous pressurized system is the increased wear of the axle seal under continuously pressurized air within an air channel extending through the seal and leading to the tires. Continuous pressurized system is not only pressurized all the time, but also tends to repeatedly fluctuate the air pressure during inflation and deflation cycles to maintain the desired pressure. Pressurized fluctuation of the air channel pressure over time adds further stress to the axle seal which disadvantageously causes premature axle seal wear and resulting failure.
The continuously pressurized system uses a simple error computation method by comparing the actual pressure to the desired pressure band, that difference activating inflation or deflation. The higher the pressure differential between the actual pressure and the desired pressure, the more the system is likely to disadvantageously overshoot the target pressure during inflation or deflation. A small orifice has been used to limit the air flow rates and reduce the time in which the system will reach the desired pressure band to reduce the amount of overshoot and undershoot. However, the smaller the orifice, the more likely the orifice is subject to blockage and failure by debris including rust, dust, dirt, or rubber from the tire, particularly for an orifice under 0.050 inches in diameter. Thus, the continuously pressurized system disadvantageously tends to overshoot or undershoot the target tire pressure, causing additional "hunting", resulting in a plurality of additional deflation or deflation actuations to reach the desired pressure band, and tends to have blocked inflation and deflation orifices, and tends to excessively wear the axle seal. Shole, U.S. Pat. No. 3,878,376 has adapted computer controls in continuously pressurized systems but disadvantageously relies upon orifice size to control air pressurization cycles which would otherwise be more precisely controlled by intelligent processing. There exists a need to reduce the "hunting" of continuously pressurized system without the required use of a small controlling orifice.
The continuously pressurized system senses a voltage indicating the desired tire pressure, and then senses a voltage indicating the actual pressure from the pressure transducer monitoring the actual pressure, and then subtracts the actual pressure from the target pressure. The system then responds to that difference by controllably actuating the inflation and deflation valves. This instantaneous difference method of the continuously pressurized system does not produce an absolute shut off after one inflation or deflation cycle to reach the target pressure. The instantaneous dynamic air pressure which deactivates an inflation or deflation adjustment cycle is different than a static air pressure reached after a small stabilization period and the adjustment cycle. This different may cause further another inflation and deflation adjustment cycles to reach and stabilize at the desired air pressure. Hence, the continuously pressurized system disadvantageously relies upon instantaneously closed loop monitoring with potential over shooting and under shooting requiring several inflation and deflation adjustment cycles to reach and maintain the desired pressure.
Continuously pressurized systems have also been subjected to power supply transients which disadvantageously affected the instantaneous difference method because that differential measurement is made with respect to the reference voltages used to determine both the desire pressure and the dynamic air pressure during inflation or deflation. The differential measurement is made continuously through an inflation or deflation pressure adjustment cycle. A voltage transient, during the inflation or deflation adjustment cycle may adversely affect the differential measurement, perhaps by a premature termination or extension of inflation or deflation period, tending to disadvantageously overshoot or undershoot, causing additions fluctuating inflation and deflation adjustment cycles. These and other disadvantages are solved or reduced using the present invention.